Typically in the production of very large scale integrated (VLSI) circuits, ultra large scale integrated (ULSI) circuits, and other microelectronic devices, aluminum is widely used as a conductive interconnect material. Alternatives to aluminum are being investigated, however, since the performance of such devices may be limited by the circuit interconnections. Copper is one such alternative, primarily because of its higher electrical conductivity and its good electromigration properties. See, for example, S. P. Murarka, in Proc. of the Workshop on "Tungsten and Other Advanced Metals for ULSI Application 1990," Eds G. C. Smith and R. Blumarthal (MRS, Pittsburgh, Pa., 1991), p. 179.
Copper, however, unlike aluminum, oxidizes rapidly, thus impacting its usefulness as interconnect material. A number of processes of passivating thin copper films have been explored, including ion implantation, formation of surface silicides, and plasma treatment. H. M. Naguib, et al., J. Vac. Sci. Tech. 13, 396 (1976); P. J. Ding, et al., Proc. MRS Symp. 260, 757 (1992); P. J. Ding, et al., J. Appl. Phys. 74, 1331 (1993); S. Hymes, et al., J. Appl. Phys. 71, 4623 (1992); P. J. Ding, et al., Proc. MRS Symp. 309, 455 (1993).
In addition, pure copper does not adhere well to insulating layers used in microelectronic devices, such as silicon dioxide (SiO.sub.2). Other techniques have explored the use of an adhesive layer to provide good adhesion between the copper and the insulating layers. Recently, the use of magnesium as a diffusion barrier to be used with copper has been investigated. B. Arcot, et al., Mat. Res. Soc. Symp. Proc. 225, 231-236 (1991). The article reports investigations of the kinetics of the phase formation sequence in copper-magnesium bilayers sputtered onto silicon dioxide on silicon substrates.
While all of these processes are effective to some degree, a process has not been developed that clearly meets all the needs of microelectronic device manufacturing, such as good conductivity, oxidation resistance and good adhesion to underlayers.